1. Field of the Invention
The present invention relates to an external fixator for immobilizing bone parts, particularly in the area of the wrist.
2. Description of Related Art
A fixator exists with which it is possible to immobilize bone parts in the area of the wrist, comprising a bar and two pin-holder assemblies which can slide and pivot relative to this bar. To allow the pins to be oriented in all the desired directions depending on the immobilization to be performed, each pin-holder assembly is mounted on a slotted ring of spherical outer shape, engaged and able to slide on the bar, and comprises two jaws, one of which is intended to receive and clamp the pins, and the other of which is intended to surround and clamp this ring.
With the second jaw in the loosened state, the ring permits each pin-holder assembly to slide along the bar and allows this assembly to pivot about the ring in the three spatial planes. Tightening of this second jaw makes it possible, by clamping the ring on the bar, to immobilize each pin-holder assembly both in terms of sliding relative to the bar and in terms of pivoting relative to the ring.
This type of fixator is satisfactory in practice but has the disadvantage of having a relatively complex structure, which is not without impact on its production cost.
This fixator cannot therefore be provided to be discarded after a single use, which means that it has to be sterilized after each use. This sterilization involves dismantling and re-fitting the fixator, which are relatively awkward operations, and requires that the fixator be kept in a suitable sterile packaging between two uses.
The present invention aims to remedy these substantial disadvantages by making available a fixator whose structure is very simple and is inexpensive to manufacture, but which nonetheless has just as many possibilities of use, in particular as regards the possibilities of spatial orientation of the pins; this structure must in particular be such that the fixator can be provided to be discarded after a single use and can be supplied in a sterilized state ready for use.
The fixator concerned comprises, in a manner known per se, a rigid bar, two pin-holder assemblies which can be moved relative to this bar, and means with which it is possible to immobilize each pin-holder assembly in a defined position relative to the bar.
According to the invention:
the bar has a cylindrical main part and a spherical part at one end;
a first pin-holder assembly comprises a one-piece body with a bore passing through it to permit its engagement by sliding on the cylindrical part of the bar; and
the second pin-holder assembly comprises a one-piece body in which a recess is formed, this recess having a zone of partially spherical shape with a radius slightly greater than that of said spherical part, this zone being such that it can receive this spherical part with pivoting, without lateral play, and with a possibility of articulation of said second pin-holder assembly.
This fixator therefore has a very simple structure and is particularly easy to manufacture. The resulting low cost allows this fixator to be used once and discarded and, consequently, makes it possible to eliminate all sterilization operations.
The first pin-holder assembly can slide and pivot relative to the bar and can therefore be placed in any required position relative to a long bone, in particular the humerus; the second pin-holder assembly is movable by pivoting relative to the bar in the three spatial planes, which permits any desired orientation of the pins, for insertion in the bone part concerned, in particular a fragment of the humerus or a metacarpal. The fixator according to the invention thus has very wideranging possibilities of movement of the pin-holder assemblies and of spatial orientation of the pins, so that its very simple structure, which is inexpensive to manufacture, does not in any way lessen its possibilities of use.
The pin-holder assemblies, by virtue of their one-piece structure, can be obtained by relatively simple cutting, drilling and tapping operations.
In addition, this fixator is quick and easy to dismantle and re-fit in a case where re-use is desired, involving sterilization.
The means by which it is possible to immobilize said first pin-holder assembly in a defined position relative to the bar preferably consist of a tapped hole formed substantially perpendicular to said bore and opening into the latter, and of a screw which can be received in this hole, this screw, when tightened, making it possible to clamp the bar in the bore.
The means by which it is possible to immobilize said second pin-holder assembly in a defined position relative to the bar can themselves consist, in an identical fashion, of a tapped hole formed substantially perpendicular to said recess and opening into the latter, and of a screw which can be received in this hole, this screw, when tightened, making it possible to clamp the spherical part of the bar in the recess.
In this case, the tapped hole opening into said recess is advantageously positioned relative to this recess in such a way that its axis is situated outside the center of said zone of partially spherical shape, toward the side of said body via which said spherical part is introduced into the recess.
The body of each pin-holder assembly preferably has at least one bore passing through it, to permit engagement of a pin, and at least one tapped hole substantially perpendicular to this bore and opening into the latter; each tapped hole receives a screw which, when tightened, makes it possible to clamp the pin in the corresponding bore in order to immobilize this pin in a defined position relative to said body.
The bar is advantageously made of a synthetic material molded to the desired shape.
This material is preferably a radiotransparent material, such as a composite material. This material is advantageously a resin reinforced with carbon fibers.
The pin-holder assemblies for their part can also be made of a synthetic material permitting sterilization by autoclave or gamma rays.
To ensure that it is clearly understood, the invention will again be described below with reference to the attached diagrammatic drawing which shows, by way of nonlimiting examples, two possible embodiments of the fixator concerned.